All posts by Simon

HP 3580A Spectrum Analyzer: Digital display fix, and ancient CMOS circuits

With most of the 3580A functions working again, we still need to fix the digital display. Essentially, the 3580A uses a digital scope circuit, similar to those use in digital oscilloscopes of the 70s.

First, some study of the ADC. The 1973 HP Journal has all the details, it is successive approximation, peak detecting ADC.

Checking the input to the digital display board, blue trace, and the comparator/approximator input to the ADC, yellow. Seems something is wrong with the ADC ciruit, or it’s timing-counter control systems.

After considerable checking and probing, I found the issue, a dead 4019 CMOS, 4×2 multiplexer. Replaced it with a “new” part, taking great care to avoid any static discharge to the board.

The dead part, it is almost a historic piece! 1974, only a few year after the introduction of CMOS circuits by RCA!

That’s the full board. Multiplayer construction. Plenty of precision resistors that are needed for the ADC circuit.

Another working antique part – the 2102 S-RAM, Intel, 1 kbit per circuit. 8 pieces – a total of 1 kbyte of SRAM!

Working display…

10 kHz reference display… Great!

Even the log scale scan is working.

One tip – put all the screws and parts in a box, and check that it is empty afterwards. So many instrumented I receive here in the workshop are missing some screws or other parts.

HP 3580A Spectrum Analyzer: a few mechanical repairs, and sweep test

With the basic functions of the 3580A restored (at least, it is sweeping again), some attention needs to be paid to the mechanics. Fortunately, all is good with the intricate tuning assembly and digital display, but the knobs have some cracks, probably, a combination of age and stress.

Everything taped up, and the cracks filled with rapid-set epoxy resin.

To apply the resin to the small cracks, you can use a piece of stiff plastic foil, cut to a tool of appropriate size –

Here, a few close-ups of the tuning mechanism. It has fast tuning, and fine tuning, a clutch, several gears – all good old analog technology.

Finally, some test of the sweep circuit – but how to test a 200 second per division (i.e. 2000 second per screen) deflection for accuracy and linearity? Well, I connected it to a 34401a multimeter, and recorded the values for several hours by GPIB interface.

As you can see, the sweep is very linear, only some minor deviation at low voltages (maybe connected to some offset voltages or similar effects of the operational amplifier), at least, we can’t see any leakage current of the capacitor, which would show up as increasing sweep time with higher voltage/later divisions.

Also interesting, see the accuracy of the sweep speed, with warm-up of the instrument (each measurement is 2000 second). Still, after all these years, well within the 5% specification of the sweep time! Amazing!

HP 3580A Spectrum Analyzer: a non-working marvel of engineering

The 3580A is a audio spectrum analyzer of the 1970s, and not only useful for audio, but anything that can be converted to audio frequencies (e.g., noise analysis of GHz sources, provided, you use the appropriate mixers). This marvel is not a FFT machine, but a discrete audio “received”, using a low-noise local oscillator, and covering a frequency range from 5 Hz to 50 kHz. The resolution filters are quarz filters, with bandwidth down to 1 Hz! Dynamic range is over 80 dB.

The device, it comes from my old university, and has been sitting there on the shelf for a while, not working. And in fact, it shows not many signs of life, it is not sweeping properly, and even in manual mode, it is not working reliably (not showing any reasonable signal, but there is some activity on the tracking output which suggests that the instrument is not all dead, also the “overrange” LED is working).

After some study and test it became clear the the issue is with the ramp generator. Unfortunately, it is not a simple ramp generator, as you can see below.

The main circuit is a capacitor being charged by a current source (mechanical switch with resistors).

The voltage at the main capacitor, a 10 µF polyester hermetic cap (really high end with glass seal and metal case), is charged and its voltage amplified by a FET-opamp (the FET input constructed from a discrete FET pair, and a PTFE stand-off to keep this all really high impedance).

All the sweeting action is controlled by a state controller, more or less, a hardwired program with several TTL chips. It took me quite some study to understand how it is supposed to work. But fact is, it doesn’t. Clearly, the issue is with the A3 assembly. This must have been quit an expensive assembly at the time, with all the FET pairs and opamps. Still today, not an easy thing to fix.

At least, it is a beautifully arranged board, all gold plated and really smells like quality. So it is worth some time and effort to fix it.

Key for such repair, at least in any reasonable time, are a set of good schematics. Fortunately, I have a set around and printed out really large copies – it is worth the effort, because without making some notes, you will struggle to keep all in your brain and still work on the circuit.

With no extender board available, just soldered some wires to the board to monitor the state of the main state counter, and some of its inputs.

Hmmm, after a lot of probing, I was almost tempted to replace a good part of the TTL chips, because it is really hard to find the defect in such a complicated and loop-wired logic circuit, including its analog parts.

But after a bit more consideration and test, I decided to try a step-wise approach, starting from the most likely parts causing issues. One of the 7473 dead, no problem, there are spares around. But the next one – a 7472! This is an AND gated J-K flip flop, with three inputs to each AND gate… in simple words, something old, exotic, and rarely used. Went through all my piles of old boards and ICs, but no 7472 to be found! Quickly arranged a temporary 7472 – from a 7411 3-input AND gate and a 7473 flip-flop.

To be sure, I tested to old 7472 – indeed, it is not working.

With the A3 board temporary fix, a quick test of the unit.

Unfortunately, still some issues, but is is sweeping:

Display issue:

Check with a X-Y scope (on the rear outputs of the 3580A) – all seems good from the analyzer section, maybe some issue with the storage display?

Finally, on xbay, found a set of 5 pcs 7472 at a reasonable price, from Spain! NOS (=new old stock), about the same age as the 3580a!

Some fluxing issue with the soldering of the old ICs (clearly seen at the 7473), beware! Use some good flux, or solder from both sides.

US TEO Power Suppy: you want to get killed by a USB charger?

This is one of the worst electronic gadgets that my workshop has every seen, a US TEO Brand A5951 USB charger. Usually, not much can go wrong with the design of a 5 V switchmode power supply, but with this device, all went wrong, a combination of bad design, bad manufacturing, and non-existing sense for product responsibility.

Can you see the wires – right hand side is low voltage side, left hand side is mains! Can you see the solder stuck to the board – almost connecting mains and low voltage?

The only “safety” function I can see if a PCB trace fuse (left hand side zig-zag) on a mildly flammable paper board.

Even the case isn’t sealed – the manufacturer is even saving the glue!

That’s the brand name and numbers, if you have one of these, take it out of service immediately!

Seems Canada has some clever authorities – they found a whole lot of unsafe USB chargers. Remember the good old days when it was illegal to import just any kind of crap?

Recipe: Pickled Garlic (and other mixed local vegetables)

This year was a good year for garlic, and all other kinds of vegetable that can handle dry (and hot!) conditions. Here is my preferred recipe for conserving these goodies for winter time:

Take about 20 bulbs of garlic
Red hot peppers (home-grown), as may as you have jars, or depending on size, some more.
3-4 mid size zucchini (from your own garden, or a friend’s garden) – remove soft inner part, cut into cube size about 3/4″
Onions, about 8 pieces, cut into irregular shapes

The jars, provide enough mid-size jars which need to be perfectly clean (best clean in dishwasher before use, even if they were cleaned before), and sterilize in boiling water (both the jars and the lids) for several minutes. Hint: add some distilled vinegar to the water to avoid formation of deposits.

For the liquid
Take 1 Liter of water, 200 mL of 25% acid white distilled vinegar, 160 g sugar, 30 g salt – bring to a boil.

Add the vegetables.

Add quantity of black pepper seeds.

Make sure that all vegetables are fully covered with the liquid, otherwise, add more liquid, or less vegetables.

Boil vigorously for at least 8 minutes.

Transfer to the jars, fill the to the top, put on the lid immediately and turn upside down (lid side down). All this must be done with boiling hot liquid and vegetables, so take care. Ensure that all jars have at least one pepper, and somewhat even balance of vegetables.

Let cool down slowly, label and store for several weeks before eating.

It is a pretty strong liquid, and it is very suitable for preserving other strong vegetables like, onion, garlic, chili, etc., and these preserve will keep several years no problem – if want to preserve light vegetables like pure zucchini, pumpkin, gherkins, etc. – lower acid concentration is advisable.

Recipe: German Küchle

One of the traditional baked goods in the Southern part of Germany: so-called Kuechle.

Recipe:
500 g wheat flour, 50 g sugar, 60 g butter, 2 eggs, 220-250 mL milk, small quantity of salt, yeast.

Prepare a yeast dough, knead it thoroughly, let it rise, knead again, and finally form small round pieces, about 15 pieces. Let rise again for 15 minutes.

For baking, heat oil (better: clarified butter) to 175-185 degrees C (ideally, use a thermometer). Then, with fingers covered with some oil or butter, pull the kuechle into shape and bake floating on the oil, turn around once the color of the 1st side is right, bake the 2nd side, then take out and put on some kitchen paper to soak-off the residual oil. Cover with some powdered sugar. Eat fresh, or freeze.

HP 8659B Spectrum Analyzer: mostly, the known issues

Mostly, the well-known issues for this 8569B: a bad fan, a bad 5.2 V supply capacitor (see the 5.2 V rail ripple below!), some issues with the display adjustment, and a bad control assembly with contact broken off. The control assembly, interestingly enough, somebody else had fixed some part of it before, from the handwriting, an American.
Still some minor issues with the Z axis control (brightness control), but this will be fixed soon, and then the analyzer will be thoroughly tested and will find good use again.

Harvest Highlights 2018: Two-continent gardening

Believe me, it is a challenge to have two gardens, one in Germany (allotment 44), one in Japan (behind the house), but after all, some good harvest results this year.

A good year for peaches in Ludwigshafen, Germany!

Many jars of jam of German blackberries, and other kinds of berries…

Japanese experiments – starting with radish, tomato, cabbage, beans, and EDAMAME (soy beans that are harvested green).

Edamame harvest… great with some beer!

Boil for 5 minutes in salt water, then cool down quickly with cold water and eat slightly cooled (don’t eat the shells!).

Pizza and Baguette Oven: From China, to Japan

One project for my new Japanese residence – a deck oven, to prepare pizza, baguette, and other baked goods, not only for myself, but also for friends, colleagues, etc.

Surprisingly, ovens, even regular household ovens, are virtually unknown in Japan. All is centered around microwaves and rice cookers, or fish grills, but nobody seems to need anything more than a small toaster oven. Well, for me, a well-working oven is absolutely essential for survival, to bake bread, pizza, and lasagne.

A deck oven, in contrast to a convection oven, transfers heat by contact and radiation more then by moving hot air around. There is a lot of science behind this, but we can leave the detail explanation to baking experts, anyway, if you want to bake a good baguette, bread, or pizza, you need a deck oven (which can have metal or stone floor – this one has metal, which is quite good for fast heat up and easy cleaning).

How to get a deck oven in Japan – it’s not easy, unless you want to pay thousands of dollars for a top brand professional imported German deck oven, or some high end Japanese equipment. Fortunately, China is close-by, and after some weeks of waiting, customs formality (You really want to import food processing equipment for use in Japan??? How come???), the big box arrived, about 100 kgs of metal and insulation. It is well build, some small shipment damage, but nothing that can’t be fixed, and it is recommended to inspect such equipment anyway, before you use it. It is from the Honglian company. YXY-10 gas deck oven, which can fit one large tray 50×60 cm easily, or three pizzas.
It has full electronic control of the heaters, digital display, high voltage pulse ignition, separate regulation of bottom and top temperature. All heavy duty. You can use steel or aluminum trays, or bake directly on a pizza mesh on the floor of the oven.

A lot of parts for little money!

Clean out the dirt and residues from manufacturing before using it. Anyway, it is a good idea to run it for a while at high temperature to get rid of all the oils and chemical residues.

Still some more work to do before firing up, electric supply installed (oven designed for 220 Volts – I also want to operate it in Germany later, but Japan has 100 Volts only), but the gas supply system (LPG) still needs some work, stay tuned!

Moving to Japan: Busy times…

Recently, not so much activity in the workshop, for a simple reason – I was moving to Japan. Still keeping the German main workshop, it is only a temporary work assignment, but temporary can mean two or three years in this case. Anyway, Japan is a great place and this move is to the real Japan, Ube, Yamaguchi, not some expat community in a big international city.

With the help for kind colleagues and the big enterprise, all has been set up in the meantime and life is carrying on along the usual path…

The Japanese house, it is of traditional style, which means, it is hot in summer and cold in winter, but at least you get a better connection to nature, and it is a very healthy life to have fresh air and wind moving trough the big open windows rather than to sit in a hermetically close skyscraper.

Not to miss, the Japanese garden!

… Vegetable garden …

The temporary workshop – I can’t go to such far away places without at least a phase noise measurement test set.

My latest acquisition, an electro-mechanical device called “Toyota Aqua”, aka Prius C – very good fuel efficiency, thanks to its hybrid drive train. Sorry, no service manual for this one but it’s great to explore the beauty of Yamaguchi Prefecture.